1. Field of the Invention
The present invention is concerned with anti-reflective coatings including polymers comprising unreacted epoxide groups, and methods of using those coatings with low dielectric constant materials to inhibit or avoid via or photoresist poisoning normally associated with those materials.
2. Description of the Prior Art
The integrated circuit industry is continually moving towards denser device integration and faster device switching speeds. Through advanced semi-conductor processing techniques, integrated circuit devices with submicron feature sizes (i.e., less than 0.35 xcexcm) can now be manufactured. This trend towards reduced feature size has, in turn, driven the need for multilayer interconnects.
The dual damascene process is a multi-level interconnection process in which, in addition to forming the grooves of the single damascene process, conductive contact or via holes are formed as well. In this scheme, circuit performance increasingly becomes a function of delay time of electronic signals traveling between the millions of gates and transistors present on an integrated circuit chip. Until recently, the integrated circuit R-C delay that determines device switching speeds was dominated by the CMOS transistor drive capacitance and load resistance. For submicron devices, the increase in signal delay due to capacitance of multilayer devices has become a limitation to improving device performance. To meet the speed and decreased crosstalk requirements for multilayer interconnect devices, it is desirable to use insulating materials having low dielectric constants (i.e., less than about 3.8) between metal interconnection lines. Some materials which have dielectric constants lower than 3.8 are disclosed in U.S. Pat. No. 6,054,380, incorporated by reference herein.
While use of these dielectric materials has been considered, they have not yet been incorporated into integrating circuit production lines. One of the primary technical difficulties preventing the use of these materials is a problem known as via poisoning or photoresist poisoning (see e.g., U.S. Pat. No. 6,103,456, incorporated by reference herein). A typical dual damascene process involves optical lithography techniques. In processes using a low dielectric constant material, the process would involve successively applying a barrier layer, a low dielectric constant layer, a hard mask layer, and an anti-reflective layer on a semiconductor substrate. Thereafter, the anti-reflective layer and low dielectric constant layer (also referred to as the low k dielectric layer) are patterned by photolithography with a photoresist layer to create openings or trenches. However, via or photoresist poisoning which occurs as a result of the low k dielectric material lying beneath the organic anti-reflective material has hindered the removal of the photoresist from the openings in the anti-reflective material. As this opening is critical to the subsequent steps of forming multilayer interconnects, the inability to clear the photoresist interferes with quality device fabrication.
The present invention overcomes the problems associated with via or photoresist poisoning by providing anti-reflective coating compositions which inhibit and/or block this poisoning.
In more detail, the compositions comprise light attenuating compounds or chromophores which can be physically mixed in the composition, reacted with some of the epoxide rings present in the polymer(s) of the composition, and/or otherwise bonded with some or all of the polymers present in the composition, so long as the compositions comprise unreacted or intact epoxide rings in the quantities recited below.
In one preferred embodiment, the compositions include a polymer which comprises: recurring monomers comprising an epoxide ring reacted with a light attenuating compound so as to open the epoxide ring (e.g., one of the carbon atoms of the ring has bonded with an atom of the light attenuating compound); and recurring monomers comprising unreacted epoxide rings (i.e., closed or intact epoxide rings). In another embodiment, the opened and intact epoxide rings are present on in different polymers.
Regardless of the embodiment, the molar ratio of unreacted epoxide rings present in the composition to reacted epoxide rings present in the composition is preferably from about 10:90 to about 90:10, more preferably from about 20:80 to about 80:20, and even more preferably from about 20:80 to about 50:50. These ratios are essentially the same in the cured composition as well. The average molecular weight of the polymer(s) is generally from about 1,000-15,000 Daltons, and more preferably from about 3,000-5,000 Daltons.
In a particularly preferred embodiment, the polymer comprises recurring monomers selected from the group consisting of 
wherein R comprises a light attenuating compound.
Preferred light attenuating compounds comprise a moiety selected from the group consisting of carboxylic acids, phenols, and amines, with a particularly preferred light attenuating compound being 9-anthracene carboxylic acid.
The polymers are preferably prepared by partially grafting an epoxy resin (or other polymer in applications where the light attenuating compound is not bonded with the epoxide moieties) with the light attenuating compound. One skilled in the art will appreciate that any known grafting process is suitable, so long as it achieves the desired epoxide ring levels as described above. The resulting polymers can then be used to prepare the anti-reflective compositions by dissolving or dispersing the polymers in a suitable solvent system. In applications where part or all of the light attenuating compound is physically mixed with the polymer(s), the light attenuating compound is also dissolved or dispersed in the solvent system.
The solvent system should have a boiling point of from about 100-180xc2x0 C., and preferably from about 120-150xc2x0 C. The amount of polymer dissolved in the solvent system is preferably from about 2-15% by weight polymer, and more preferably from about 3-7% by weight polymer, based upon the total weight of the composition taken as 100% by weight. The solvent system should be utilized at a level of from about 85-98% by weight, and more preferably from about 93-97% by weight, based upon the total weight of the composition taken as 100% by weight. Preferred solvent systems include a solvent selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, propylene glycol n-propyl ether, and mixtures thereof.
The inventive compositions can further include a crosslinking agent. This can be accomplished by the use of a crosslinking agent separate from the polymer or, alternately, the polymer can include xe2x80x9cbuilt-inxe2x80x9d crosslinking moieties. Preferred crosslinking agents include those selected from the group consisting of melamine and glycouril crosslinking agents. The crosslinking agent or moieties should be present in the composition at a level of from about 0.2-5% by weight, and preferably from about 0.5-1% by weight, based upon the total weight of all ingredients in the composition taken as 100% by weight. Thus, the anti-reflective compositions should cross-link at a temperature of from about 85-250xc2x0 C., and more preferably from about 100-220xc2x0 C.
It will be appreciated that numerous other optional compounds can be incorporated into the inventive anti-reflective or fill compositions if desired. Such other optional ingredients include 4,4xe2x80x2-sulfonyl diphonol and pyridinium tosylate.
The anti-reflective coatings are applied according to conventional processes (e.g., spincoating), and can be used in conjunction with any low k (less than about 3.8) dielectric material including fluorinated silicate glass, amorphous-fluorinated carbon, fluorinated polyimides, fluorinated polyarylene ethers, and parylene-F.